Conventionally, a motor drive device is widely used in refrigeration equipment such as air conditioners, and industrial machines. The motor drive device includes a rectifier circuit configured to convert an alternating current voltage supplied from an alternating power supply into a direct current voltage and an inverter configured to convert the direct current voltage from the rectifier circuit into an alternating current voltage.
In this motor drive device, in the case where a single-phase alternating current voltage or three-phase alternating current voltages are converted into a direct current voltage at a diode rectifier circuit, voltage ripples are generated in the direct current voltage. The voltage ripples have a frequency component twice or six times an alternating power supply frequency fs inputted to the rectifier circuit. The voltage ripples can be reduced when the capacity of a smoothing capacitor connected on the output side of the rectifier circuit is increased. However, an increase in the capacity of the smoothing capacitor causes an increase in the cost and volume of the motor drive device, which is a problem.
In the case where voltage ripples are present in the direct current voltage, the output voltage of the inverter includes a direct current voltage ripple frequency ωrip component due to influence, such as the detection delay of the direct current voltage and the arithmetic operation delay of an inverter controller. Thus, the distortion of the motor current is generated.
Specifically, in the case where the resistance r of the winding wire of the motor driven by the inverter or the inductance L of the motor is small, when the output frequency of the inverter comes close to the direct current voltage ripple frequency, “the frequency component that is the difference” between these two frequencies generates the distortion of the motor current and a large pulsating current, resulting in a beat phenomenon in which the output torque of the motor pulsates.
An example of a method of eliminating this beat phenomenon is disclosed in PTL 1. PTL 1 discloses a method in which the high frequency component of a γ-δ axis current in a rotating coordinate system is detected, three-phase current beat (distortion) components are operated, the operated values of these components are amplified, and then three-phase voltage command values are corrected.